Electron guns having at least one emissive cathode surface and one nonemissive electrode adjacent said cathode surface



April 39, 1968 .1. ARNAUD ETAL ELECTRON GUNS HAVING AT LEAST ONEEMISSIVE CATHODE SURFACE AND ONE NONEMISSIVE ELECTRODE ADJACENT SAIDCATHODE SURFACE 5 Sheets-Sheet 1 Filed Aug. 10, 1965 INVENTORS:

J-A/P/VAUZ? AFGWE/VDT ATTORNEY April 30, 1968 J. ARNAUD ETAL 3,381,155

ELECTRON GUNS HAVING AT LEAST ONE EMISSIVE GATHODE SURFACE AND ONENONEMISSIVE ELECTRODE ADJACENT SAID CATHODE SURFACE Flled Aug 10, 1965 5Sheets-Sheet 2 IN V E NTORSZ JARA/A U0 8 6. WE/VDT ATTORNEY J. ARNAUDETAL ELECTRON GUNS HAVING AT LEAST ONE EMISSIVE April 30, 1968 CATHODESURFACE AND ONE NONEMISSIVE ELECTRODE ADJACENT SAID CATHODE SURFACE 5Sheets-Sheet 5 Vol Filed Aug. 10, 196

INVENTORS:

JAR/VA U0 A 6. WE/VDT ATTORN EY United States Patent 3,381,155 ELECTRONGUNS HAVING AT LEAST GNE EMISSIVE CATHODE SURFACE AND ONE NONEMlSSWEELECTRGDE ADJACENT SAID CATHODE SURFACE Jacques Arnaud and Georg Wendt,both of 79 Blvd. Haussmaun, Paris Seme, France Filed Aug. Ill, 1965,Ser. No. 478,577 Claims priority, application France, Aug. 26, 1964,986,210 9 Claims. (Cl. 313-82) ABSTRACT OF THE DISQLGSURE An electrongun producing, without any focusing magnet acting on the gun space, anelectron beam having a substantially linearly variable electron densityover its cross-section, this density varying between substantially zerovalue near the axis of the beam and a maximum value near the peripheryof the cathode. The gun comprises at least one emissive cathode surfacetilted at substantially 67 with respect to the axis, and at least onenonernissive electrode having an edge adjacent the peripheral edge ofthe cathode surface, and forming therewith an angle of substantially157.

'l' he present invention relates to electron guns generating electronbeams, in particular to those for use in high power travelling wavetubes. It aims at realizing an electron gun capable of generating a beamhaving in its crosssection an electron density progressively increasingfrom one point of this cross-section toward at least one boundary linethereof forming the cross-section of at least one lateral surface of thebeam.

It is known in the art that when an electron beam interacts with thedelay line of a travelling wave tube, the conditions of interaction arebetter when the portion of the beam relatively nearest to the delay linehas an electron density which is as high as possible. Therefore, it isclear that when, for instance, the beam has a circular cross-section andmoves through the interior of a delay line having an annularcross-section, the conditions of interaction would be better if theelectron density varied from the center toward the periphery of thecross-section, that is, if the density were substantially zero along theaxis of the beam and progressively increased to become maximum near thelateral surface thereof, as compared with a beam having a constantelectron density throughout all points of its crosssection. However, inthe prior art only guns generating constant-density beams are known,such as a circular beam with constant density at all points of itscircular cross-section, or an annular beam with constant density at allpoints of the annulus representing its crosssection, or a fiat orribbon-like beam with constant density at all points of the rectanglerepresenting its cross-section.

Accordingly, it is an object of the present invention to produceelectron guns generating electron beams having over their cross-sectionsuch an electron density distribution that a relatively betterinteraction condition with a delay line of a travelling wave tube isattained, as compared to the known constant-density electron beams.

Another object of the present invention is to produce ice a gungenerating a ribbon-like electron beam having a progressively variableelectron density from one of its flat surfaces to the other.

Still another object of the present invention is to produce a gungenerating a ribbon-like electron beam having a progressively increasingelectron density distribution from the center thereof toward both fiatlateral surfaces.

A further object of the present invention is to produce a gun generatingan electron beam having a symmetry of revolution, in which the electrondensity distribution progressively increases from the axis thereof, orfrom a circle of predetermined diameter surrounding the axis, toward thelateral surface thereof.

These and other objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawing, which shows forpurposes of illustration only, several embodiments in accordance withthe present invention and wherein:

FIGURE 1 is a partial transverse cross-sectional view of a gungenerating an electron beam in the form of a double ribbon;

FIGURE 2 is a partial transverse cross-sectional view of a gungenerating a single variable-density ribbon-like beam;

FIGURE 3 is a partial transverse cross-sectional view of a gungenerating a variable density electron beam having a symmetry ofrevolution, and

FIGURE 4 is a partial transverse cross-sectional view of an alternativeof the gun as shown either in FIGURE 1 or in FIGURE 3, wherein a portionof the emissive surface of the cathode is suppressed, thereby obtaininga hollow fiat or circular beam.

The present invention essentially consists of means whereby the cathodeof an electron gun is caused to emit electrons with a substantiallylinearly increasing density from a region of its surface remote from theperiphery, toward the said periphery, together with means foraccelerating the electrons to cause them to flow in a pr determineddirection, the space between the cathode and the accelerating meansbeing free of any magnetic field. Such structure has the property thatthe paths of the accelerated electrons converge asymptotically towardthe axis of the said direction to form a variable density beam. Theeffect of such beams, when used to pass parallel to a delay line of atravelling wave tube, is to improve the conditions of interaction withthis line, and consequently to increase the etficiency and gain when thetube is operated as an amplifier, or to increase the output powerthereof when the tube is operated as an oscillator.

More specifically, the guns according to the present invention include acathode having at least one emissive surface tilted with respect to thedesired direction of the beam, associated with at least one non-emissiveelectrode, the angle between the non-emissive surface of the lastnamedelectrode and the emissive surface of the cathode having a predeterminedvalue dependent on relative potentials of the electrode and cathode, andthe angle between the emissive cathode surface and the axis extending inthe desired direction having also a well-defined value, which is,however, different for plane and rotational structures, respectively Inthe case of a plane structure,

' the emissive surface is a plane forming with the axis an angle ofsubstantially 67. Moreover, a pair of such surfaces may be disposedsymmetrically to the axis, thereby forming a dihedral with an angle ofsubstantially 134 between the two surfaces. In the case of a structurehaving a symmetry of revolution, the emissive surface is a cone thesurface of which forms with the axis an angle of substantially 45 thatis a cone having an opening angle of substantially 90.

Referring now to the drawing, and more particularly to FIGURE 1,reference numerals 1 and 2 designate therein two plane metallic surfacesof a cathode which are electron-emissive when heated by any conventionalmeans (not shown). These surfaces intersect along an edge 3, therebyforming a dihedral having an opening angle of substantially 134. Thelength of the dihedral in the direction perpendicular to the drawing,i.e., the width of the beam to be produced, is unlimited so that a beamhaving a very high intensity may be obtained. To avoid spreading of thebeam in the direction of its width, conventional terminal electrodes maybe provided, these electrodes being not shown herein as they form nopart of the present invention. Reference numerals 4 and 5 designate twolateral non-emissive electrodes, having a shape which is easilydetermined by those skilled in the art to define the position of twoextreme paths 6 and 7 between which it is desired that the beam becontained. Assuming that these electrodes are carried, by conventionalmeans (not shown), at the same potential as the cathode surfaces 1 and2, a value of substantially 157 will be given to the angle between thesurfaces 4 and 1, or 5 and 2, respectively. However, the same paths 6and 7 could be obtained with electrodes 4 and 5 biased negatively orpositively with respect to the surfaces 1 and 2, provided that acorresponding alteration, readily determinable by those skilled in theart, is made either in the shape of the electrodes 4 and 5, or in theirangle with respect to the surfaces 1 and 2.

Perpendicular to the bisecting plane 8 of the dihedral, and at adistance from the edge 3 which is determined solely by the desiredconvergence to be given to the beam, is located an anode 9 carried byany conventional means (not shown) at a suitable positive potential withrespect to the cathode surfaces 1 and 2. This anode is made of soft ironwith a View toward magnetically shielding the space between the cathode1, 2 and the anode 9, so that the electrons emitted from the cathodemove in a space free of any magnetic field. The paths of differentelectrons emitted by the cathode are contained between two extreme paths6 and 7 and form a beam which passes through a rectangular slot 10provided in the anode 9, and thereafter enters into the space beyondthis anode.

It is assumed, without any intention of limit-ing the present inventionto such application that this space is an interaction space of a linearO-type travelling wave tube having a double delay line. For the sake ofsimplicity, and by reason of the conventional nature thereof, no elementof this tube has been shown, except its two parallel delay lines 11 and16. A longitudinal magnetic field is established in this space as in anyconventional O-type tube, but this field does not penetrate into thespace of the gun because of the shielding action of the anode 9. It isassumed that both lines 11 and 16 are properly excited in phase, andthat their interaction with the beam moving between the two lines 11 and16 in the direction of the arrow 12 is coherent. No other detail of thetravelling wave tube has been shown, as such details are of entirelyconventional nature.

A theoretical study made by the applicant on the described structure hasascertained its following properties:

(1) The current emitted from any given point of the cathode surfacevaries substantially linearly with the distance between this point andthe edge 3; its intensity is zero along this edge, therefore there areno electrons moving within the bisecting plane 8, while its maximum liesin the inception points of the paths 6 and 7.

(2) Various intermediate paths such as 13, 14, 15, etc. convergeasymptotically toward the bisecting plane 8, without any point ofcross-over if the cathode is at the potential of ground, i.e., if theinitial velocities of the electrons are zero.

(3) The beam entering into the space beyond the anode 9 has in itscross-section a variable density, the current being zero in thebisecting plane 8, provided that the initial velocities are zero.Therefore, the electrons are focused to form a beam in the form of twoparallel ribbons separated by an electron-free region near the plane 8,the densities in each ribbon increasing moreover from their innersurfaces toward their outer surfaces defined by the extreme paths 6 and7.

This last-named property is extremely advantageous for the purpose ofinteraction with the delay lines 11 and 16. Taking for sake ofcomparison a ribbon-like beam having the same width but uniform electrondensity, and assuming the same amount of power applied to the beam, itis readily seen that in the beam produced by the means according to thepresent invention, the electromagnetic field is concentrated near theouter surfaces of the ribbons, that is in a region of the beam which isrelatively nearest to the delay line; it is known that under theseconditions the efiiciency of cumulative energy transfer is improved, sothat the tube is able to operate with relatively higher amplificationgain or with relatively higher oscillatory power output, under theassumption of equality of all other operational parameters.

Referring now to FIGURE 2 wherein like reference numerals as in FIGURE 1are used to designate like parts, there is shown a structure wherein ahalf of the electrode system of FIGURE 1, that is the emissive electrode2 and the non-emissive electrode 5, have been suppressed. There aremaintained in this embodiment the electrode 1, forming with the plane 8an angle of substantially 67, and the electrode 4 forming with theelectrode 1 an angle of substantially 157, provided both electrodes arecarried at a common potential. A calculation made by applicants showsthat the electrons emitted from the surface of the cathode 1 follow thesame paths 6, 13, 14, 15 as in FIGURE 1, provided that the samedistribution of electric field and potential as in FIGURE 1 is restored.According to the present invention, this distribution is restored byreplacing the emissive electrode 2 by a non-emissive electrode 17forming an angle of substantially 45 with the plane '8, so that thedihedral defined by the surfaces 1 and 17 has an opening angle ofsubstantially 112. Moreover, the anode 9 has its lower half suppressedand replaced by an electrode 18 in the form of a hyperbolic cylindricalsuface. As a result thereof, the electrons emitted from the cathode 1are concentrated to form a single ribbon-like beam with non-uniformelectron density, passing above the plane 8. This beam could be used forinteraction with a single delay line 11.

The same principles are applied according to the present invention togun systems having a symmetry of revolution. The emissive cathodeelectrode is then a cone as indicated by reference numeral 19 in FIGURE3. Applicants calculation has shown that the same properties asdescribed above are maintained if the opening angle of the cone is ofsubstantially i.e., if the cathodic surface forms an angle ofsubstantially 45 with the axis of the cone. In front of the base of thecone is located a non-emissive electrode 29, having a symmetry ofrevolution and a suitable profile, with an opening of substantially thesame diameter as the base of the cone 19. The surface of the electrode20 forms with the internal surface of the cone 19 an angle ofsubstantially 157 provided both electrodes are carried at a commonpotential. The function of the electrode 20 is the same as that of theelectrodes 4 and 5 in FIGURE 1. The electrons emitted from the cathode19 are then concentrated to form a variable density cylindrical beam 21having zero density along its axis. This beam passes through theaperture 10 in the anode 9 and may thereafter be used to pass throughthe interior of a helix 22 operating as delay line of a travelling wavetube.

It is not necessary that the cathodic emissive surface of the examplesdescribed above extend up to the edge 3 or to the apex of the cone 19,since the electron emission in the vicinity of this edge or apex is verysmall so that the corresponding emissive area of the cathode could besuppressed without substantially reducing the total current intensityemitted from the cathode. Thus, FIG- URE 4 shows a cross-section of acathode electrode which might correspond, for instance, either to theplane structure of FIGURE 1 or to the rotational structure of FIG- URE3, wherein a portion of the emissive surface neighboring the edge of thedihedral or the apex of the cone has been suppressed, thus leaving anaperture 23. However, in order to maintain the described properties, thesame distribution of electric field and potential as in the precedingfigures should be restored. This is done by providing a non-emissiveelectrode 24 having its edge facing the periphery of the aperture 23.The shape, potential and angle with respect to the cathode surface aredetermined for this electrode by calculation or experimentation by anymeans known to those skilled in the art, so that the same fielddistribution is restored as for the same configuration without aperture23 and without electrode 24. The behavior of the gun is then the same asin the preceding figures, and the beam generated by this gun has thesame property of non-uniform electron density.

While we have shown and described several examples of embodiments inaccordance with the present invention, it is understood that the same isnot limited thereto but is susceptible of numerous changes andmodifications as known to a person skilled in the art, and we thereforedo not wish to be limited to the details shown and described herein butintend to cover all such changes and modifications as are encompassed bythe scope of the appended claims.

We claim:

1. An electron gun for generating an electron beam, comprising emissivecathode means having a periphery and a region remote from saidperiphery, and means for emitting by said cathode means an electroncurrent with substantially linearly increasing density from said remoteregion toward said periphery, thereby generating an electron beam Withvariable electron density over its crosssection, and anode means foraccelerating the electrons to cause the same to flow in a predetermineddirection, said anode and cathode means defining a space substantiallydevoid of a magnetic field, an aperture being provided in said anodemeans to enable the flow therethrough of said electrons to form a beam,and a utilization space beyond said anode means for utilizing said beam,wherein said cathode means includes at least one substantially planeemissive surface tilted with respect to said direction at angle ofsubstantially 67, and at least one nonemissive electrode located nearsaid periphery and forming an angle of substantially 157 with thesurface of said cathode means, said beam being ribbon-like and means forcarrying said cathode means and said non-emissive electrode means at acommon potential.

2. An electron gun for generating an electron beam, comprising emissivecathode means having a periphery and a region remote from saidperiphery, and means for emitting by said cathode means an electroncurrent With substantially linearly increasing density from said remoteregion toward said periphery, thereby generating an electron beam withvariable electron density over its crosssection, and anode means foraccelerating the electrons to cause the same to how in a predetermineddirection, said anode and cathode means defining a space substantiallydevoid of a magnetic field, an aperture being provided in said anodemeans to enable the flow therethrough of said electron to form a beam,and a utilization space beyond said anode means for utilizing said beam,wherein said cathode means includes a pair of plane emissive surfaceslocated in planes intersecting along a straight line forming edge of adihedral having an opening angle of substantially 134, saidpredetermined direction being substantially located in the bisectingplane of said dihedral substantially perpendicular to said edge, saidbeam being in the form of double ribbon, and a pair of non-emissiveelectrode means located respectively near each periphery of both of saidemissive surfaces opposite said edge, and each forming with therespective emissive surface an angle of substantially 157, means beingprovided for carrying both said emissive surfaces and both saidnon-emissive electrode means at a common potential.

3. A gun as claimed in claim 2, wherein .both said emissive surfaces areextended to physically intersect along said edge.

4. A gun as claimed in claim 2, wherein both said emissive surfaces arelimited on the side of said edge by a periphery, both of said lastmentioned peripheries defining a slot in the apex of said dihedral, andauxiliary electrode means having an edge facing each of said peripheriesto obtain a predetermined distribution of electric field.

5. An electron gun for generating an electron beam, comprising emissivecathode means having a periphery and a region remote from saidperiphery, and means for emitting by said cathode means an electroncurrent with substantially linearly increasing density from said remoteregion toward said periphery, thereby generating an electron beam withvariable electron density over its cross-section, and anode means foraccelerating the electrons to cause the same to flow in a predetermineddirection, said anode and cathode means defining a space substantiallydevoid of a magnetic field, an aperture being provided in said anodemeans to enable the flow therethrough of said electrons to form a beam,and a utilization space beyond said anode means for utilizing said beam,wherein said cathode means includes at least one substantially planeemissive surface tilted with respect to said direction at angle ofsubstantially 67, and at least one non-emissive electrode means locatednear said periphery and forming an angle of substantially 157 with thesurface of said cathode means, and said nonemissive electrode means at acommon potential, and a plane non-emissive electrode tilted with respectto said direction by an angle of substantially 45 and forming with saidplane emissive surface an angle of substantially 112.

6. A gun as claimed in claim 5, wherein said anode means includes aportion in the shape of hyperbolic cylindrical surface, said anodeportion extending, with respect to the plane passing through theintersection line of said emissive and non-emissive surfaces andcontaining said predetermined direction, on the same side of said planeas said non-emissive electrode.

7. An electron gun for generating an electron beam, comprising emissivecathode means having a periphery and a region remote from saidperiphery, and means for emitting by said cathode means an electroncurrent with substantially linearly increasing density from said remoteregion toward said periphery, thereby generating an electron beam withvariable electron density over its crosssection, and anode means foraccelerating the electrons to cause the same to flow in a predetermineddirection, said anode and cathode means defining a space substantiallydevoid of a magnetic field, an aperture being provided in said anodemeans to enable the flow therethrough of said electrons to form a beam,and a utilization space beyond said anode means for utilizing said beam,wherein said cathode means include at least one emissive surface tiltedwith respect to said direction, and at least one nonemissive electrodemeans located near said periphery and forming an angle of substantially157 with the surface of said cathode means, said emissive surface beingthe internal surface of a cone having an opening angle of substantiallysaid beam being of cylindrical shape with a substantially electron-freeregion along its axis.

8. A gun as claimed in claim 7, wherein means are pro- 7 8 vided forcarrying said cone and said non-emissive elec- References Cited trodemeans at a common potential, and wherein said UNITED STATES PATENTSangle between the surfaces of said cone and of said non- 2 268 19612/1941 Pierce 313*82 emissive electrode means is of substantially 157.2843776 7/1958 Tien T X A gun as claimed in claim wherein said is 5 2936 396 5/1960 Currie 313-s2 x cut near its apex substantiallyperpendicular to its axis 2:996:64O 8/1961 Eichenbaum to form asubstantially circular hollow base, and auxiliary electrode means havingan edge facing the circumference HERMAN KARL SAALBACH, P imary Examiner.of said base, said auxiliary electrode means being located ELI LIEBERMANExaminer within said cone to obtain a predetermined electric field 10distribution. P. L. GENSLER, Assistant Examiner.

